The present invention relates to apparatus for maintaining stacks of superimposed sheets which consist of paper or the like. More particularly, the invention relates to apparatus for treating stacked sheets of paper or the like preparatory to or during transport to packing or other processing stations.
It is well known that stacks of superimposed sheets tend to undergo more or less pronounced deformation during transport from the stacking station or stations to the processing station or stations. The tendency of stacks to undergo deformation is especially pronounced when the stacks must be diverted from their normal path, when the deflection is pronounced (e.g., through an angle of 90.degree.), and/or when the stacks are abruptly accelerated or decelerated irrespective of whether such changes in speed take place during movement along a straight path or during deflection from such path. If the configuration of a stack departs from its optimum (normally parallelepiped) shape, the stack is not likely to fit into a receptacle or it cannot be properly processed to form part of or to constitute a steno pad, an exercise book or another stationery product. For example, if one marginal portion of a stack of overlapping paper sheets is formed with a row of holes for introduction of a helical binder which is made of wire or the like, the binder cannot be introduced into the holes in an automatic machine if the sheets of the stack are not in accurate register with one another.
It has been found that a major cause of the tendency of paper sheets in a stack to move relative to one another is that the stack contains pockets of air which are entrapped between certain neighboring sheets and act not unlike layers of lubricant by facilitating the movements or by promoting the tendency of sheets which flank an air pocket to move relative to each other. As a rule, at least a certain percentage of entrapped air will escape with time. However, the damage is normally done before the escape of appreciable quantities of air is completed, especially in a modern high-speed paper processing machine wherein the intervals for transport of successively assembled stacks from the stacking station to the next processing station are very short. Furthermore, it is normally desirable to locate the first processing station close or very close to the stacking station; this also reduces the length of intervals which are available for spontaneous escape of air from pockets between certain sheets of the stack.